1. Field of the Invention
The invention generally relates to a lens, and more particularly, to a zoom lens.
2. Description of Related Art
The zoom lens is a common optical component of an optical system, which may be used in a wide variety of applications including digital cameras, back projection televisions, projectors, or the like. In general zoom lenses, aspheric lenses are used for reducing the total number of the lenses in a zoom lens, such as U.S. Pat. Nos. 6,738,196, 7,061,688, and 6,147,812. However, the aspheric lenses have little tolerance, thereby increasing the difficulty in fabrication and assembly. Moreover, the aspheric lenses have larger cost. Other zoom lenses adopt more zooming lens groups for reducing the total number of the lenses in a zoom lens, and avoid using aspheric lenses, such as U.S. Pat. Nos. 6,906,867, 6,894,845, and 6,137,638. However, the more the zooming lens groups are, the larger the cost of the zoom lens is.
Taiwan Patent No. M281179 discloses a zoom lens in FIG. 2B. The zoom lens has ten lenses, and includes a first lens group having a negative refractive power and a second lens group having a positive refractive power. The first lens group is composed of four lenses, and the four lenses respectively have positive, negative, negative, and positive refractive powers. The second lens group is composed of six lenses. In addition, Taiwan Patent No. I288290 discloses a zoom lens in FIG. 1. The zoom lens has eleven lenses and includes a first lens group having a negative refractive power and a second lens group having a positive refractive power. The first lens group is composed of four lenses, and the second lens group is composed of seven lenses.